Analysis of the mechanism of action of preoperative bilirubin that causes cognitive impairment after liver transplantation: verification of permeability of high-concentration bilirubin

Abstract

Background: We previously found an association between preoperative bilirubin concentration and cognitive impairment after liver transplantation. In order to study a possible mechanism for bilirubin causing postoperative cognitive dysfunction, we investigated the effect of high concentrations of bilirubin on the blood–brain barrier. Methods: Our model system was 30-week-old transgenic zebrafish fabp10a:cfp-NTR. In preliminary experiments we confirmed systemic absorption after retro-orbital injection using reddish Rhodamine-dextran injected with a Hamilton syringe. For the hyperbilirubinaemia model we used retro-orbital injection of bilirubin, with subsequent measurement of bilirubin concentration in the brain and blood. Food reward learning was conducted for 4 days using the T-maze, and learning cognitive ability videos were filmed without food reward on the 5th day (control group=9/bilirubin group=9). Again using Fabp10a:cfp-NTR zebrafish, methimazole was injected to damage the liver, and after 3 and 7 days, the brain was extracted and stained with Evans blue to check the blood–brain barrier permeability. Results: In the T-maze test, there was no difference between the bilirubin and control groups (P=0.4135). There was no statistically significant difference in the bilirubin level measured in the brain after retro-orbital injection of bilirubin on the 1st, 2nd, and 3rd days between the 10-fold and 50-fold injection groups. However, bilirubin measured in blood decreased over time as blood concentrations increased. As a result of Evans blue staining, there was no difference in colour between the 3rd and 7th day brains compared with the control (Fig. 9). Conclusion: As a result of this study, cognitive dysfunction occurs when liver damage occurs, but this seems to occur even without a change in blood–brain barrier permeability, and bilirubin is not considered to be the sole cause of cognitive dysfunction.